Electric motor.



No. 63l,9l9. I Patented Aug. 29, I899.

R. ARNU.

ELECTRIC MOTOR.

(Application filed Mar. 5, 1898.)

(No Model.)

1m: moms PETERS c0.. Padre-mun, mswmnmm n. c

UNITED STATES PATENT OFFICE.

RICCARDO ARNO, OF TURIN, ITALY.

ELECTRIC MOTOR.

SPECIFICATION forming part of Letters Patent No. 631,919, dated August29, 1899.

Application filed March 5, 1898.

To all whom it may concern-.-

Be it'known that I, RICGARDO ARNO, a subject of the King of Italy,residing at Turin, in the Kingdom of Italy, have invented certain newand useful Improvements in Electric Motors; arid I do hereby declarethat the following is a full, clear, and exact description of the same.

The asynchronous monophase alternatingcurrent motors heretofore knownare started by superimposing upon the alternating field an oblique fielddiffering in phase. Their field-magnet, or what is termed the stator,(see PoZg phase Electric Cmvcnts, by S. P. Thompson, 1895, page 112,)consists of two groups of coils, one of said groupsz'. 6., the maincoi1sbeing fed by the alternating lnonophase current, which is to keepthe motor in motion while it performs useful Work. The other group ofcoils-the auxiliary starting-coi1s-receive current which only flowsthrough them while the motor is being started, said current being out ofstep with that in the main coils.

The object of my invention is to dispense with the auxiliarystarting-coils and provide simple and eilicient means for starting andreversing the motor.

I have discovered that by inserting an additional resistance into theclosed-coil armaturei. c. the rotor (according to the nomenclatureintroduced by Prof. S.P.Thompson)- and by imparting to said rotor orarmature an initial motion of very low speed, such as may be obtained byturning it by hand, asynchronous monophase motors can be started withoutthe use of a rotating magnetic field and only one group of coils-thatis, the main coils-need be fed with current. The motor thus acts as anasynchronous monophase motor during the period of starting, just asmotors fitted with the starting-gears heretofore in use do after theyhave got up speed and the auxiliarystartingcoilshave been switched out.This observation has led me to construct a new asynchronous monophasemotor provided with only one set of coils on the stator, the auxiliarystarting-coils being dispensed with. This motor is started by insertinginto the closed-coil armature (rotor) an additional resistance and animpulse given to the rotor by hand, the motor running in Serial No.672,664.. (No model.)

that direction in which the impulse was given. The said additionalresistance must be capable of admitting of gradual reduction, so as tobe switched out gradually and without shocks just before the motor hasgot up speed.

Under these conditions the strength of cur rent during the whole periodof starting will at no time exceed the value it takes just as as themotor begins to turn. Trials carried out on large motors of, say, onehundred horsepower and more under no load except the friction of thebelt and loose pulley prove that the additional resistance that is to beinserted in the armature to cause the motor to proved motor withstarting devices attached,

and Fig. 2 is a similar view of the armature (rotor) coils, brushes, andrings.

I have found that theoretically the value of the resistance to beinserted in the elementary armature-coils is 0 :.414. 27mL, wherein nrepresents the frequency of the alternating magnetic field and r and Lthe resistance and the induction of each of the elementaryarmature-coils, respectively. The value of r: 21mL is the greatest valuethat r can have in order to give positive values of torque correspondingto positive values of the speed for alternatingpolyphase'currentmachines. I have found that the value of the resistance to be insertedin the rotor-coil circuits of asynchronous alternating monophase currentmotors practically about one-half and more exactly .414 times thatmaximum resistance which, if inserted in the armature of the-motorconsidered as a polyphase machine, will just allow it to act as a motor.This maximum or critical resistance, if increased, will cause themotor-coils to have such a resistance as to cause the machine to thenact as a generator instead of as a motor. This agrees i with the resultsof my trials above referred to. l and nnmediatcly atte'rwaid at 72.

I have shown, for the purpose of illnstrat ing my invention, in Fig. 1 adiagrannnatic view of a motor having a two-pole stator, each pole havingonly a single coil carrying an alternating monophase current, and inFig. 2 also a diagrammatic view, the rotor provided with a three-phasewinding, the three coils electrically connected to rings on which trailbrushes, these brushes being connected, as shown in Fig. 1, with asuitable resistance adapted to be gradually cut out of circuit. Thus farthe device is adequate to start the motor provided a slight impulse isgiven to the rotor by hand, the direction of which impulse determinesthe direction of run.

in the practical operation of machines of this class it is objectionableto the operators to have to move the rotating part by manual force, so Ihave further illustrated means whereby this objection is overcome. Itwill be observed that I have no auxiliary winding on the stator to beused as a starting-coil.

S S is a bipolar stator supplied from the circuit P Q bya monophascalternating current. The coils of the motor closed at O are connected tothe rings 1 2 3, on which trail the brushes (1' [0 Each of these coils SS S is connected through its respective ring and brush to a resistance RR R adapted to be cut out by turning the three-armed lever O on therheostat through the gradually-reducing resisttances a 1) e (Z. Themaximum resistance which I insert is 0 0.41% 211111 or 0AM times thegreatest value that will still allow the machine to act as a motor. Thisresistance is such that when inserted in the rotor-coils and a smalldegree of rotation is given the rotor by hand the motor will beself-starting, as the circuit is gradually cut out as the motor assumesnormal speed.

To obviate the necessity of starting the rotor by an impulse given it byhand, I have shown diagrammatically means whereby this can beaccomplished.

7; is the cut-outfor the main circuit. 7b is a cut-out for one of theeoilssay S and "i is a cut-out fora second coilsay S. It will besullicient to say for the purposes of this invention that 7; and 7t aresuccessively closed by a switch K, the particularconstruction andarrangement of mechanical devices employed for accomplishing this resultforming no part of my invention. It is also unimportant what particularmeans or device is used for closing the switch 2'. The object of thesedevices is to render the rotor-coils unsymmetrical at the instant ofstarting, and this is done by having one of said coils on open circuit,which will be sul'ficient to cause the starting of the machine, providedit be not at a dead-point, the cut-out i being in this case not used.The

stopping of the machine at a dead-point can always be avoided by ajudicious operator. It follows that if the motor is not at the deadpointit will only be neccssaryto operetc the switch K, whereby the circuit isclosed at The current passing to the stator lirst acts tor a very shortperiod on the rotor while one of its coils (shown in the drawings as S)is in open circuit. This is sutficient to cause the rotor to make apartial turn to give the necessary impulse to the moving part, when thecircuitin the open coil is then closed and the motor slowly started, theresistance in the three coils being then gradually cut out until normalspeed is produced. This result maybe greatly increased by causing theresistance in the closed coils to be comparatively small at the timewhen the cut-out It is closed, then closing the open coil at 71,increasing the resist ance in the outer coils to a maximum, andgradually cutting out the resistance in all the coils as the motorassumes normal speed.

I will now suppose that the motor is at the dead-point and I wish tostart it without giving it an impulse or partial turn by hand.

For this purpose I open the switch at 2 placing the coil S on opencircuit. his will give me two coils S and S on open circuit. Then byoperating the switch K one of the active coils S will cause the rotor toturn through a slight angle. Immediately afterward coil S will be put incircuit and the motor will tend to assume a deadpoint with regard tothese two coils when the other coil is put in circuit by closing thecut-out i, when the motor will be started, the resistance in all thecoils being then gradually cut out as the motor assumes normal speed.This process also affords a convenient means for reversing the directionof the motor, in which case it will only be necessary to provide meansfor breaking the circuit in the coil S instead of in coil S, and thenstart in the manner above described.

Having thus described my invention, what I claim as new therein, anddesire to secure by Letters Patent, is--- 1. A method of startingasynchronous monophase alternating-eurrent motors,which consists ininserting a suitable resistance in the rotor-coils and momentarilyrendering the coils of the rotor unsymmetrical and gradually cutting outthe resistance, substantially as and tor the purpose set forth.

2. A method of startingasynchronous monophase altemating-currentmotors,which consists in inserting a suitableresistance in therotor-coils, momentarily placing one or more of the rotor-coils on opencircuit and then gradually cutting out the resistance, substantially asand for the purpose set forth.

A method of startingasynchronous monophase alternating-currentmotors,which consists in inserting in the rotor-coil circuits aresistance of (Ll-Lt times the maximum just allowing the machine to actas a motor when considered as a rotary field-motor imparting a slightimpulse to the motor, and gradually cutting out such resistance,substantially as set forth.

l. A method of starting asynchronous monophasealternating-current1notors,which consists in inserting a suitableresistance in the rotor-coil circuits, rendering the coils of the rotorunsymmetrical by placing some of them on open circuit, successivelyclosing them When current is supplied to the motor, and graduallycutting out the resistances, substantially as and for the purpose setforth.

5. A method of starting asynchronous monophase alternating-currentmotors,which consists in inserting in the rotor-coil circuits aresistance of r .414 X .ZrmL giving the motor a slight impulse andgradually cutting out the resistance, substantially as and for thepurpose set forth.

6. A method of starting asynchronous monophase alternatin g-eurrentmotors,which con RIOOARDO ARNO.

Witnesses:

SANTE ZIRRCO, OTTORINO SARRAINO.

